In a typical electrophotographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member. The latent image is subsequently rendered visible by application of electroscopic thermoplastic resin particles which are commonly referred to as toner. The visible toner image is then in a loose powdered form and is usually fused, using a fusing apparatus, upon a support, which may be an intermediate member, or a print medium such as plain paper.
Conventional fusing apparatuses include a fuser member and a pressure member, which may be configured to include a roll pair maintained in pressure contact or a belt member in pressure contact with a roll member. In a fusing process, heat may be applied by heating one or both of the fuser member and the pressure member.
Fuser members can be coated with layers (e.g., topcoat) of materials having low surface energy (to maintain good release properties), adequate flexibility, good thermal conductivity, and/or mechanical robustness (to extend fuser member life). Fluoropolymer such as perfluoroalkoxy (PFA) resins are often used in topcoats for fuser members because they possess both low surface energy and high mechanical strength.
PFA topcoats are usually prepared as coatings by spray coating or dip coating from aqueous dispersions, powder coating with PFA powders, or as sleeves by extruding PFA resins. As perfluoroplastics such as PFA, PTFE and FEP are highly crystalline fluoropolymers, they are typically insoluble in organic solvent and melt at high temperatures, i.e. about 260 to about 327° C.
Among the coating processes available for topcoat application—including spray coating, flow coating, power coating, and dip coating—flow coating has advantages over other processes because it permits high transfer efficiency (e.g., flow coating provides a more efficient metered coating process, resulting in less wasted coating material, as compared to spray coating which involves overspray loss), high production rate, and avoids toxic airborne atomized PFA particles. Employing flow-coating methods for applying PFA resin particles and like fluoroplastics in dispersion can be difficult compared to spray or dip coating methods. This is because flow-coating has relatively strict conditions for the coating dispersion to be stable and to have suitable rheology.
One example of a stable flow-coatable fluoroplastic topcoat formulation is taught in U.S. Pat. No. 8,588,669, issued on Nov. 19, 2013, to Qi Zhang et al., which includes common inventors with the present disclosure. However, it has been found by the inventors of the present disclosure that when carbon nanotubes are included in the fluoroplastic topcoats of the Zhang patent, flow coating followed by a high temperature baking process results in large voids on the surface and undesirable agglomerates throughout the coating. It is believed that these defects indicate an incompatibility with the nanotube dispersion system being employed.
A novel flow coating composition or flow coating method for manufacturing nanotube/fluoroplastic composites suitable for use as fuser topcoat materials and/or for solving one or more of the aforementioned problems would be considered a notable advancement in the art.